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Infrared Lasers Resulting from Giant Pulse Laser Excitation of Alkali Metal Molecules
1.P. P. Sorokin and J. R. Lankard, J. Chem. Phys. 51, 2929 (1969).
2.C. R. Vidal and J. Cooper, J. Appl. Phys. 40, 3370 (1969).
3.Briskeat Samox tapes, for example, work up to 1600 °F (871 °C).
4.The role of the wick is also vital when the vapor cell is charged with helium and is therefore not operating in the heat‐pipe mode. The wick still draws condensed metal vapor back to the center of the oven and prevents it from freezing out at the two ends of the cell.
5.F. W. Loomis and P. Kusch, Phys. Rev. 46, 292 (1934).
6.P. Kusch and M. M. Hessel, J. Mol. Spectry. 32, 181 (1969).
7.Also seen on the original plates corresponding to Fig. 2 are diffuse maxima at 0.827 and 0.834 μ representing Cs‐He satellite bands and four weak diffuse bands between 0.817 and 0.873 μ first reported in Ref. 5 and later studied in more detail in Ref. 6. In Ref. 1 it was erroneously stated that these four bands taken collectively were comparable in strength with the λ7667 band. This error on our part arose first of all from lack of consideration of the role of helium in broadening the resonance lines and creating various satellites of the latter. (An atmosphere of He was generally used in the measurements of Ref. 1.) Second, the fact that it is impossible to determine relative absorption strengths of two totally absorbing bands was generally overlooked in Ref. 1 [O. Jefimenko and S. Y. Ch’en, J. Chem. Phys. 26, 913 (1957)].
8.With the same ruby laser and heat‐pipe oven used to obtain the data of Fig. 3 a peak beam intensity of at 3.095 μ was obtained from the distal end of the tube for a ruby beam imput power of a pressure and a close to optimum temperature of 280 °C. At least twice this infrared output power would be received if an infrared reflecting mirror were placed between the ruby laser and heat‐pipe oven and aligned to the former.
9.O. S. Heavens, J. Opt. Soc. Am. 51, 1058 (1961).
10.See for example, A. R. Striganov and N. S. Sventitskii, Tables of Spectral Lines of Neutral and Ionized Atoms (IFI/Plenum, New York‐Washington, 1968).
11.When a broadband dye laser operating in the vicinity of 8000 Å was used to excite helium‐buffered cesium vapor, prominent absorption bands at 7944, 8016, and 8079 Å were detected in the dye laser beam transmitted through the cell. These wavelengths correspond to the transitions and respectively. The bands became more intense when the wavelength of the dye laser emission was shifted to shorter wavelengths where, of course, the molecular band strongly absorbs (Fig. 2). This suggests that perhaps quenching of the laser emission shown in Fig. 5 results from collisional dissociation of molecules excited to the state. Molecules excited to highlying vibrational levels of could conceivably be dissociated into either 6p or 5d states upon undergoing collision with helium atoms. However, the same three absorption lines are seen also when helium buffer gas is excluded from the region of cesium vapor, i.e., when the vapor cell is operated in the heat‐pipe mode. Under these conditions the lines are much less broadened, of course. The above implies that while some collisional dissociation into 6p and 5d states may occur at the higher helium pressures, two‐step absorption by molecules followed by dissociation will also always cause some atoms to be placed into these states. The collisional dissociation model, incidentally, fails to explain why infrared laser action occurs at 3.095 μ. rather than at when ruby is used to pump helium‐buffered cesium vapor. This is because the ruby beam does not directly excite the state. The fact that there is no infrared laser beam at either 3.095 μ or when pure cesium vapor is pumped by a ruby laser alone could be explained by assuming that two‐quantum absorption by molecules primarily produces excited Cs 8p atoms, due to the increased photon energy of the pumping beam in this case. According to recent work [Y. Ono, I. Koyano, and I. Tanaka, J. Chem. Phys. 52, 5969 (1970)] an 8p Cs atom has a large cross section for colliding with a ground state Cs atom to produce plus an electron. Thus the flow of atoms from the 8p states to the state would normally be impeded. With helium buffer gas present, however, frequent collisions with He atoms would greatly enhance this flow thus enabling lasing to occur from the state.
12.M. Pimbert, J. Pascale, and J. Berlande, Abstracts of Papers, Proc. Intern. Conf. Phys. Electron. At. Collisions, 6th, Cambridge, Mass., 1969, 670 (1969).
13.The addition of helium increases the width of alkali metal lines in linear fashion, up to at least several tens of atmospheres. At one atmosphere of buffer gas the half‐width of the main resonance lines is between 0.5 and [S. Y. Ch’en and M. Takeo, Rev. Mod. Phys. 29, 20 (1957)].
14.An estimate of the absorption coefficient at the center of the lines based upon previously derived formulas [D. S. Hughes and P. E. Lloyd, Phys. Rev. 52, 1215 (1937)] leads to a value corresponding to a mean free path ∼2 mm. Here the 6p density is assumed to be The oscillator strength is taken to be ∼0.1, and a collision broadened linewidth is assumed. This shows that radiation trapping should not prevent oscillation at the power levels being discussed here. Evidently this is the case, since the long pulses are observed [Fig. 6(a)].
15.D. Grischkowsky, Phys. Rev. Letters 24, 866 (1970).
16.G. A. Askar’yan, Zhetf Pis. Red. 4, 400 (1966);
16.[G. A. Askar’yan, JETP Letters 4, 270 (1966)].
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